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Synthesis and physical-chemical study of sandwich-type heteropolyoxometalate with dinuclear vanadium clusters

M. HOSSU1, D. RUSU2, M. RUSU2, D. COZMA1, L. DAVID1,* , O. COZAR1

Affiliation

  1. Babes-Bolyai”Univ., Dept. of Physics, 400084,Cluj-Napoca, Romania
  2. Medical and Pharmaceutical Univ., Dept. of Chem.-Phys., Cluj-Napoca, Romania

Abstract

The sandwich-type K10[(VO)2Sb2W20O70]⋅20H2O heteropolyoxotungstate was investigated by means of elemental analyses, thermogravimetric and spectroscopic (FT-IR, UV−VIS and EPR) methods. The analysis of vanadium ion coordination mode was made comparing the FT-IR spectrum of the complex with the Na9[BiW9O33]⋅14H2O ligand. The stretching vibration of the terminal W=Ot bonds is shifted with 8 cm−1 towards higher wave numbers in the FT-IR spectrum of the complex , which indicates the involving of the terminal oxygen atoms in the coordination to the vanadium ions. The νas(W−Oe−W) vibration is shifted with 11 cm−1 in complex FT-IR spectrum. This behavior arrises from different deformations induced by the vanadium ions coordination in the frame of the trilacunary ligand. The decrease of the νas(W−Oe−W) frequency in complex indicates the stretching of these bonds after the metallic ion complexation. The shift of νas(Bi−Ob,c−W), νs(W−Ob−W), νas(W−Oc−W) bands in the complex comparative to the ligand is due to the substitution of the lateral WO6 octahedra by the (VO)O4 square pyramid and the coordination of (VO)II ions at Ob,c type oxygens. In UV spectra, the charge transfer pπ(Oc,e)→dπ*(W) band is shifted in complexes compared to the ligands spectra with ≈ 245 cm−1 towards higher wavelength. Visible spectra contain the 2B2(dxy) → 2E(dxz,yz) and 2B2(dxy) → 2B1(dx2 − y2) transition bands for vanadyl ions in C4v local symmetry, at 12040 cm−1 and respectively 14705 cm−1 for the complex. The powder EPR spectrum obtained in the X band at room temperature are typical for mononuclear oxovanadium species in an axial environment. The spectrum exhibits eight components both in the perpendicular and in the parallel bands (g⊥ = 1.973, gII = 1.912, A⊥ = 69.5 G, AII = 201.6 G)..

Keywords

Heteropolyoxotungstates, VO complex, FT-IR spectroscopy, UV-VIS spectroscopy, EPR spectroscopy.

Submitted at: Feb. 25, 2008
Accepted at: Aug. 28, 2008

Citation

M. HOSSU, D. RUSU, M. RUSU, D. COZMA, L. DAVID, O. COZAR, Synthesis and physical-chemical study of sandwich-type heteropolyoxometalate with dinuclear vanadium clusters, Journal of Optoelectronics and Advanced Materials Vol. 10, Iss. 9, pp. 2346-2350 (2008)